The removal or separation of lead from other metals has been both a primary and a secondary object of various metal recovery schemes.
For example, U.S. Pat. No. 1,918,817 issued to C. L. Mantell is primarily concerned with the removal and recovery of lead which is present as coatings in tubes, template and scrap for example. In accordance with this patent, lead is separated from an underlying metal by chemical dissolution of the lead in either a saturated aqueous sodium chloride solution containing from 0.5-10% sulphuric acid or acid sulphates; a 1-10% FeCl.sub.3, 2-10% NaNO.sub.3 solution; a 1-10% NACl, HCl and 2-10% NaNO.sub.3 solutions; or solutions containing soluble sulphates, nitrates and acetates in combination.
Similarly, U.S. Pat. No. 2,839,390 addresses the removal of lead and zinc from their ores by chemical dissolution. Here, lead and zinc, if not already in the form of their sulfides, e.g., in galena and sphalerite, are converted to their sulfides. The sulfides are then reacted with oxalic acid converting the lead and zinc to their respective oxalates and evolving H.sub.2 S gas. The product is filtered and the filter cake containing the oxalates is treated with an aqueous calcium acetate solution resulting in the formation of soluble lead and zinc acetates and insoluble calcium oxalate. The calcium oxalate precipitate is collected and reacted with sulfuric acid to regenerate oxalic acid while the solution is reacted with zinc so as to precipitate lead from the solution while forming more zinc acetate. The zinc may then be recovered by adding calcium hydroxide to the solution.
In still another process of commercial interest, lead recovery is not the primary object, however lead is an impurity which often must be separated from the desired metals to achieve the desired purity. Therefore, the lead removal may be said to be secondary to (albeit necessary) the recovery of the primary metals. Such a process occurs, for example, in the treatment of tankhouse slime for the recovery of copper and precious metals, e.g., gold, silver and palladium. Tankhouse slime is the residue which results or collects during the electrolytic deposition of copper. This residue generally contains lead impurities which must be removed in order to recover pure precious metals which are also present in the slime. One commercial procedure employed in such recovery processes can be found with reference to an article entitled "Recent Methods for the Treatment of Anodic Slimes of Copper Electrolysis" by F. Habashi appearing in Metallurgia, December 1965, pp. 257-263. However, this article is not directed to lead separation.
A very recent article in Chemical Abstracts Vol. 98, 1983, page 224, which article postdates the work of the inventors herein, teaches lead removal from decoppered anodic slime by leaching the lead containing solution with ammonium acetate solution and then crystallizing lead acetate.